Intracellular Ca 2C stores play a central role in the regulation of cellular [Ca 2C ] i and the generation of complex [Ca 2C ] signals such as oscillations and waves. Ca 2C signalling is of particular significance in sperm cells, where it is a central regulator in many key activities (including capacitation, hyperactivation, chemotaxis and acrosome reaction) yet mature sperm lack endoplasmic reticulum and several other organelles that serve as Ca 2C stores in somatic cells. Here, we review i) the evidence for the expression in sperm of the molecular components (pumps and channels) which are functionally significant in the activity of Ca 2C stores of somatic cells and ii) the evidence for the existence of functional Ca 2C stores in sperm. This evidence supports the existence of at least two storage organelles in mammalian sperm, one in the acrosomal region and another in the region of the sperm neck and midpiece. We then go on to discuss the probable identity of these organelles and their discrete functions: regulation by the acrosome of its own secretion and regulation by membranous organelles at the sperm neck (and possibly by the mitochondria) of flagellar activity and hyperactivation. Finally, we consider the ability of the sperm discretely to control mobilisation of these stores and the functional interaction of stored Ca 2C at the sperm neck/midpiece with CatSper channels in the principal piece in regulation of the activities of mammalian sperm.Reproduction (

Ca2+i signalling is pivotal to sperm function. Progesterone, the best-characterized agonist of human sperm Ca2+i signalling, stimulates a biphasic [Ca2+]i rise, comprising a transient and subsequent sustained phase. In accordance with recent reports that progesterone directly activates CatSper, the [Ca2+]i transient was detectable in the anterior flagellum (where CatSper is expressed) 1–2 s before responses in the head and neck. Pre-treatment with 5 μM 2-APB (2-aminoethoxydiphenyl borate), which enhances activity of store-operated channel proteins (Orai) by facilitating interaction with their activator [STIM (stromal interaction molecule)] ‘amplified’ progesterone-induced [Ca2+]i transients at the sperm neck/midpiece without modifying kinetics. The flagellar [Ca2+]i response was unchanged. 2-APB (5 μM) also enhanced the sustained response in the midpiece, possibly reflecting mitochondrial Ca2+ accumulation downstream of the potentiated [Ca2+]i transient. Pre-treatment with 50–100 μM 2-APB failed to potentiate the transient and suppressed sustained [Ca2+]i elevation. When applied during the [Ca2+]i plateau, 50–100 μM 2-APB caused a transient fall in [Ca2+]i, which then recovered despite the continued presence of 2-APB. Loperamide (a chemically different store-operated channel agonist) enhanced the progesterone-induced [Ca2+]i signal and potentiated progesterone-induced hyperactivated motility. Neither 2-APB nor loperamide raised pHi (which would activate CatSper) and both compounds inhibited CatSper currents. STIM and Orai were detected and localized primarily to the neck/midpiece and acrosome where Ca2+ stores are present and the effects of 2-APB are focussed, but store-operated currents could not be detected in human sperm. We propose that 2-APB-sensitive channels amplify [Ca2+]i elevation induced by progesterone (and other CatSper agonists), amplifying, propagating and providing spatio-temporal complexity in [Ca2+]i signals of human sperm.

Generation of NO by nitric oxide synthase (NOS) is implicated in gamete interaction and fertilisation. Exposure of human spermatozoa to NO donors caused mobilisation of stored Ca 2+ by a mechanism that did not require activation of guanylate cyclase but was mimicked by S-nitroso-glutathione (GSNO; an S-nitrosylating agent). Application of dithiothreitol, to reduce protein -SNO groups, rapidly reversed the actions of NO and GSNO on [Ca 2+ ] i . The effects of NO, GSNO and dithiothreitol on sperm protein Snitrosylation, assessed using the biotin switch method, closely paralleled their actions on [Ca 2+ ] i . Immunofluorescent staining revealed constitutive and inducible NOS in human oviduct and cumulus (the cellular layer investing the oocyte). 4,5-diaminofluorescein (DAF) staining demonstrated production of NO by these tissues. Incubation of human sperm with oviduct explants induced sperm protein S-nitrosylation resembling that induced by NO donors and GSNO. Progesterone (a product of cumulus cells) also mobilises stored Ca 2+ in human sperm. Pre-treatment of sperm with NO greatly enhanced the effect of progesterone on [Ca 2+ ] i , resulting in a prolonged increase in flagellar excursion. We conclude that NO regulates mobilisation of stored Ca 2+ in human sperm by protein S-nitrosylation, that this action is synergistic with that of progesterone and that this synergism is potentially highly significant in gamete interactions leading to fertilisation.

The contribution of receptor-operated Ca2+ channels (ROCs), voltage-operated Ca2+ channels (VOCs), and intracellular Ca2+ release to contractions induced by a range of stimuli in the guinea pig isolated trachea has been evaluated. In the presence of physiological Ca2+ (1.3 x 10(-3) M), tissue pretreatment with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) (4 x 10(-3) M for 5 min) markedly inhibited (> 90%) the contractile responses to a range of agonists. Therefore, under physiological Ca2+ concentration, Ca2+ mobilization from internal stores appeared to make little contribution to maximum contractions. Nifedipine (10(-7) M) or verapamil (10(-5) M) abolished KCl-induced contractions but produced variable inhibition of contractions induced by other agonists. The ROC (and VOC) blocker, SK&F 96365 (10(-5)-10(-4) M), inhibited both KCl-induced contractions and the nifedipine-insensitive component of contractions induced by acetylcholine (ACh), U46619, or leukotriene D4 [half maximal inhibitory concentration (IC50) values 1.7-3.8 x 10(-5) M]. Ni2+, which has ROC- and VOC-blocking actions, also abolished nifedipine-insensitive contractions induced by ACh. When Ca2+ was replaced with Ba2+, the contraction induced by ACh was blocked by nifedipine. Also, under these conditions, ACh did not increase the KCl maximum contraction. These data are consistent with there being distinct ROC and VOC influx pathways in guinea pig trachea and with ROCs playing a significant role in smooth muscle contraction.

Fluorescence microscopy of cells loaded with fluorescent, Ca 2+ -sensitive dyes is used for measurement of spatial and temporal aspects of Ca 2+ signaling in live cells. Here we describe the method used in our laboratories for loading suspensions of human sperm with Ca 2+-reporting dyes and measuring the fluorescence signal during physiological stimulation. Motile cells are isolated by direct swim-up and incubated under capacitating conditions for 0-24 h, depending upon the experiment. The cell-permeant AM (acetoxy methyl ester) ester form of the Ca 2+ -reporting dye is then added to a cell aliquot and a period of 1 h is allowed for loading of the dye into the cytoplasm. We use visible wavelength dyes to minimize photo-damage to the cells, but this means that ratiometric recording is not possible. Advantages and disadvantages of this approach are discussed. During the loading period cells are introduced into an imaging chamber and allowed to adhere to a poly-D-lysine coated coverslip. At the end of the loading period excess dye and loose cells are removed by connection of the chamber to the perfusion apparatus. The chamber is perfused continuously, stimuli and modified salines are then added to the perfusion header. Experiments are recorded by time-lapse acquisition of fluorescence images and analyzed in detail offline, by manually drawing regions of interest. Data are normalized to pre-stimulus levels such that, for each cell (or part of a cell), a graph showing the Ca 2+ response as % change in fluorescence is obtained. Video LinkThe video component of this article can be found at http://www.jove.com/video/1996/ ProtocolSperm from healthy fertile males, with a normal semen analysis, are normally prepared for imaging as follows. .8 Na lactate) supplemented with 0.3% charcoal de-lipidated/fatty acid free Fraction V BSA (quality of the BSA is crucial for successful capacitation of sperm). 1 ml of sEBBS is pipetted into each of a series of 5 ml tubes and gently underlayered with 0.3 ml of semen. After incubation for 1 hour (37°C; 6% CO 2 ) the top 0.7 ml is gently removed from each tube and pooled. 10 μl of the sperm suspension is diluted with 90 μl of 1% (v/v) formalin to immobilize the cells, then sperm are counted in a Neubauer chamber. Cell density in the suspension is then adjusted (with sEBSS) to 6 million cells/ml. 2. The sample is then divided into aliquots of 200 μl in loosely-capped tubes and incubated (37°C; 6% CO 2 ) in for 5-6 h to allow capacitation. 3. Coverslips (22x50 mm) have previously been treated with poly-D-lysine. 10 μl of poly-D-lysine solution (10% w/v) is applied as a number of small drops to the centre of the coverslip. The poly-D-lysine is then allowed to air dry. This can be on a heated stage and should be to complete dryness. A coverslip is attached with vacuum grease to an enclosed, purpose-built, perfusable, polycarbonate imaging chamber (dimensions 35 mm x 20 mm x 5 mm; capacity ≈ 180 μl) similar to the Warner RC20 chamber .The poly-D-lysine-coated coverslip forms the base ...

BackgroundBackground rates of latent tuberculosis infection in low prevalence regions of Britain are unknown. These would be valuable data for interpreting positive IGRA results, and guiding cost-benefit analyses. The management of a large outbreak of tuberculosis occurring in a rural district hospital provided an opportunity to determine the background rates and epidemiology of IGRA-positivity amongst unselected hospital patients in a low-prevalence region of U.K.MethodsAs part of a public health surveillance project we identified 445 individuals exposed to the index cases for clinical assessment and testing by a TB-specific interferon-γ release assay (IGRA): T-Spot.TB. Uniquely, an additional comparator group of 191 age-matched individuals without specific recent exposure, but with a similar age distribution and demographic, were recruited from the same wards where exposure had previously occurred, to undergo assessment by questionnaire and IGRA.ResultsRates of IGRA positivity were 8.7% (95%CI, 4.2-13, n=149) amongst unexposed patients, 9.5%(3.0-22, n=21) amongst unexposed staff, 22%(14–29, n=130) amongst exposed patients, 11%(6.1-16, n=142) amongst exposed staff. Amongst the individuals without history of recent exposure to the outbreak, IGRA-positivity was associated with prior TB treatment (OR11, P.04) and corticosteroid use (OR5.9, P.02). Background age-specific prevalences of IGRA-positivity amongst unexposed individuals were: age <40 0%(N/A), age 40–59 15%(12–29), age 60–79 7.0%(1.1-13), age≥80 10%(5.9-19).ConclusionsBackground rates of IGRA-positivity remain high amongst unselected white-Caucasian hospital inpatients in U.K. These data will aid interpretation of future outbreak studies. As rates peak in the 5th and 6th decade, given an ageing population and increasing iatrogenic immunosuppression, reactivation of LTBI may be a persistent hazard in this population for several decades to come.

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